1. Field of the Invention
The present invention relates generally to arrangements for erecting structures on uneven sites such as an ocean floor, and more particularly to an arrangement in which at least one structural member is formed by two elongate sections axially slidable relative to one another, and wherein the sliding movement is prevented at a desired time after erection of the structure so as to fix the length of the structural member.
2. Description of the Known Art
When erecting construction-related structures at places of difficult access, like the ocean floor or on mountainous ground, it is frequently found that the actual levels of different bases for the structure do not coincide with those initially assumed. Such inaccuracies sometimes occur due to difficulty in determining the exact morphology of the bearing strata. Differential settlements of distinct foundations once test loads are applied on different columns, also account for discrepancies between the assumed and the actual base levels.
In such cases it is necessary to underpin some bases, in order to keep all the bases at the levels assumed in the initial structural design. But underpinning is very difficult or impossible to accomplish in sites having difficult access. The only solution is to modify the length of some members of the structure, in order to overcome differences between the assumed and the actual structural configuration.
FIG. 1 represents an elemental structure formed by three rigid columns 1, 2 and 3, inter-connected by bracings 8 and 9, and rigidity diagonals 4, 5, 6 and 7.
FIG. 2 shows a condition in which an actual foundation plane for column 2 is at a lower level than the foundation plane for the bases of columns 1 and 3. As shown, the structure will tend to deform, and the members 4, 5, 6, 7, 8 and 9 will adopt the positions at 4a, 5a, 6a, 7a, 8a & 9a. Thus, if the base for column 2 cannot be underpinned, the members 4a, 6a, 8a and 9a must be lengthened while the members 5a and 6a must be shortened, as shown in solid lines in FIG. 2, in order to maintain the columns 1, 2 and 3 in a vertical position.
It will be understood that if the lengths of the mentioned members are not modified in FIG. 2, tension or compression stresses will arise. Such stresses, alone or combined with the regular loads that the members must withstand according to the initial design, can surpass the limits allowed and, eventually, lead to the destruction of some of the structural elements. It is mandatory, in such cases, to modify the lengths of almost all the connecting elements to meet the exact dimensions required by the actual structural configuration, thus avoiding abnormal stresses that may be provoked in different structural members by deformation of the construction.
To readjust all connecting members at an exact final length, delicate and troublesome operations would be necessary, using special clevises, turnbuckles, right-hand and left-hand thread bolts, sleeve nuts, slicing clamp plates and the like. Under certain conditions, as when the foundation is on an ocean bed in deep waters, such length-adjusting operations would be impossible to accomplish. When possible, these operations are nonetheless time-consuming and very costly, sometimes requiring the use of divers and special equipment. Bad oceanographic or atmospheric conditions make these difficulties grow worse. Storms, high waves, currents, very low temperature waters, heavy winds, rain, and very cold or hot atmospheric conditions can make it completely impossible to implement correcting operations for the lengths of structural members, making it necessary to suspend all work.